Transfer mold for reducing ram flash

ABSTRACT

A ram transfer mold having a plurality of channel areas in the bottom wall extending between and interconnecting the plurality of sprue holes in order to permit raw material to flow laterally therealong as the ram is forced into the reservoir and into an extremely close spaced relationship with the bottom wall. The channel areas permit the ram to approach the bottom wall more closely than heretofore possible and reduce the scrap ram flash generated during each heat.

I United States Patent 11 1 1111 3,764,248 Hall Oct. 9, 1973 TRANSFERMOLD FOR REDUCING RAM 2,883,704 4/1959 Jurgeleit 425/250 X FLASH3,557,270 1/1972 Waid 264/328 x [75] Inventor: Harold E. Hall,Middlefield, Ohio FOREIGN PATENTS OR APPLICATIONS [73] Assignee: StewartRubber Company Bedford, 994,417 11/1951 France 425/245 Oh'o 1 PrimaryExaminerJ. Spencer Overholser Flledi p 1971 Assistant Examiner-David S.Safran [21] APPL Nu2 177,775 Attorney-James H. Tilberry et a1.

[52] US. Cl. 425/251, 425/DlG. 228, 425/DIGv 806, [57] ABSTRACT 264/297A ram transfer mold havlng a plurality of channel 51 1m. 01 B29f 3/10,B29h 1/00 areas in the bottom wall extending between and inter- [58]Field of Search 425/250, 251, DIG. 51, connecting the plurality of sprueholes in Order to p 425/DIG 223, 7 242, DIG 249/105, mit raw material toflow laterally therealong as the 264/297, 328 ram is forced into thereservoir and into an extremely close spaced relationship with thebottom wall. The 5 References Cited channel areas permit the ram toapproach the bottom UNITED STATES PATENTS wall more closely thanheretofore possible and reduce the scrap ram flash generated during eachheat. 2,900,663 8/1959 Lmdhorst.... 425/357 X 2,777,411 1/1957 Geisler264/328 X 4 Claims, 4 Drawing Figures I v I w A 62 ,l 8 L8 I2 14PATENTEI] URI 9 I973 PRIOR ART INVENTOR, AROLD E. HALL BY fizzy/ Y5.

1 TRANSFER MOLD FOR REDUCING RAM FLASH This application pertains to theart of molding and more particularly to transfer molding.

The invention is particularly applicable to ram transfer molds of thetype used for molding rubber products and will be described withparticular reference thereto; however, it will be appreciated that theinvention has broader applications and may be employed in otherinstances where it is desired to mold articles from other materials intransfer type molds.

Transfer molding is a term generally applied to a process of formingarticles in a closed mold from a predetermined amount of uncured rubberwhich is loaded into a material reservoir or pot and then forced througha plurality of sprue holes into a corresponding plurality of heated moldcavities by the application of pressure where the rubber is permitted tocure. This type of molding is favored in that it permits closetolerances to be held on all mold and workpiece dimensions. Also,because of the almost complete absence of flash on the articles beingmolded, the variation in dimensions from article to article is extremelyslight. However, there are certain intrinsic limitations to usingtransfer molding, that is, any ram flash or raw material remaining inthe reservoir and sprue holes following molding and curing must bediscarded as it too has been cured. Therefore, transfer molding has notbeen particularly well suited for molding quite small pieces because ofthe relatively high proportion of waste material in the reservoir andsprue holes.

The pressure to force the uncured rubber from the reservoir and into theworkpiece forming cavities is provided by a ram which is forciblyinserted into the reservoir and against the uncured rubber. Heretofore,it has been necessary to assure that the ram would not extend closerthan a certain minimum distance toward the bottom wall of the reservoirin order to permit the uncured raw material to flow laterally throughoutthe reservoir and into and through the sprue holes. If the final orclosed distance between the ram and bottom wall was less than theminimum distance, the molding process would be inefficient as theviscosity of the uncured rubber would prevent a consistent material flowfrom being realized so that certain of the workpiece forming cavities inthe mold would not be completely filled and additional scrap would thusbe generated. Because of the space required to assure proper materialflow within the reservoir during the molding process, it has become thepractice within the trade to merely accept the scrap ram flash generatedduring molding as merely being a necessary expense of using the transfermolding process.

The present invention contemplates an improved ram transfer mold whichovercomes all of the above referred problems and others and providesmeans for reducing ram flash which is simple, economical to employ, andreadily adaptable to any ram transfer mold utilizing a materialreservoir or pot.

In accordance with the present invention, there is provided animprovement for a ram transfer mold of the type wherein uncured rawmaterial is received in a reservoir disposed in the mold itself with thebottom wall of the reservoir interconnected to workpiece formingcavities. within the mold by a plurality of sprue holes. Means aredisposed in the bottom wall of the reservoir for permitting the uncuredraw material to flow within the reservoir and to the plurality of sprueholes when the ram is brought into an extremely close spacedrelationship with the bottom wall.

In accordance with a limited aspect of the present invention, the meansfor permitting material flow are a plurality of channel areas disposedso as to extend along the surface of the bottom wall.

The principal object of the present invention is the provision ofimproved ram transfer molds which reduces the amount of scrap ram flashgenerated during each heat.

Yet another object of the present invention is the provision of animprovement for ram transfer molds which reduces the amount of rawmaterial required for each heat.

Still another object of the present invention is the provision of animprovement for ram transfer molds which is readily adaptable to moldsemploying any configuration of sprue hole location within the reservoir.

Another object of the present invention is the provision of animprovement for ram transfer molds which may be readily incorporatedinto existing ram transfer molds.

The invention may take physical form in certain parts and arrangementsof parts, a preferred embodiment of which will be described in detail inthis specification and illustrated in FIGS. 2 and 3 of the accompanyingdrawings which form a part hereof and wherein:

FIG. 1 is a cross sectional schematic showing in a general way the partsand operation of a ram transfer mold;

FIG. 2 is a plan view of a ram transfer mold employing the concepts ofthe subject invention with the ram removed therefrom for ease ofillustration;

FIG. 3 is a cross sectional view taken along lines 3-3 in FIG. 2; and,

FIG. 4 is a view of the scrap ram flash generated in the reservoir andsprue holes when using a mold incorporating the concepts of the subjectinvention as shown in FIGS. 2 and 3.

Referring now to the drawings wherin the showings are for the purposesof illustrating the preferred embodiment of the invention only and notfor purposes of limiting same, FIG. 1 show a typical the prior art ramtransfer mold, and FIGS. 2 and 3 show a ram transfer mold embodiment inaccordance with the present invention, in both cases the mold beingcomprised of an upper mold half generally designated A, a lower moldhalf generally designated B and a ram generally designated C. Thesecomponents may be constructed from tool quality steel as is conventionalin the mold construction field.

The upper mold half includes a flat top portion 10 and a flat bottomportion 12 and the lower mold half includes a flat top portion 14 and aflat bottom portion 16. Disposed in bottom portion 12 are a plurality ofupper workpiece cavity areas 18 which are interconnected with a rawmaterial reservoir or pot 22 by sprue holes 24. Generally, the cavityareas are identical with each other in order that a plurality ofidentical workpieces may be molded in one operation and, in FIG. 1 andFIG. 3, are merely generally shown and do not represent cavity areas forany particular workpiece. The specific number of cavity areas may varydepending on the size of the workpiece to be formed and the mold size,with 50 such cavities not being uncommon. Reservoir 22 includes a bottomwall 28 and continuous side wall 30. It should be noted that thedimensions and configurations of the reservoir, sprue holes and cavityportions are well known in the art and that the sprue holes may includea conical lead-in area 29 adjacent bottom wall 28 to provide for ease ofmaterial flow as is also known in the art.

Lower mold half B includes a plurality of lower cavity areas 40oppositely disposed from cavity areas 18 and runners 44 asscoiatedtherewith in order to connect the cavity areas with sprue holes 24. Itis to be appreciated that each combination of cavity areas 18 and 40form a separate workpiece forming cavity. Again, as the specities of thecavities do not form a part of the present invention, they are not morefully described or shown.

Ram C includes a generally flat bottom 50 and an outer peripheralsurface 52. The dimension of the surface 52 is such that it may beclosely received in reservoir 22 against continuous side wall 30 thereofas is known in the art.

In using the above described ram transfer mold, ram C is generallymounted stationarily on a press and upper and lower mold halves A and Bare both mounted for selective generally vertical reciprocation in thedirections designated a and b in FIG. I. The means for effecting thisreciprocation may be provided by any of several types of pressesgenerally utilized in the rubber molding industry and which do not forma part of the present invention and are therefore not shown in detail.It should be further noted that lower mold half B is movable verticallydownward a greater distance than upper mold half A in order that the twohalves may be separated for removing finished workpieces as willhereinafter become more readily apparent.

To use. the mold as shown in FIG. 1, the mold halves are moved to theirlowermost vertical position in direction 12 so that there is a spaceprovided between ram C and the upper mold half for inserting the rawmaterial into reservoir 22 and a space between the upper and lower moldhalves so that the previously molded workpieces may be removed. Apremeasured, generally by weight, amount of uncured rubber R which hasbeen formulated, as is known, to accommodate a particular workpiecerequirement is placed in reservoir 22. The lower mold half is then movedvertically upward until it contacts and carries with it the upper moldhalf. With the meeting of the mold halves at bottom and top portions 10,14, the corresponding cavity areas 18, 40 form the plurality ofworkpiece forming cavities interconnected with reservoir 22 by sprueholes 24 and runners 44. Together, the mold halves are further directedupwardly until ram C engages reservoir 22 with outer peripheral surface52 being closely received relative to continuous side wall 30. As themold halves are further directed upwardly, the ram enters further intothe reservoir so that flat bottom 50 acts against the premeasuredquantity of uncured rubber thereby forcing the raw material laterally toand then through sprue holes 24 and runners 44 into the associatedworkpiece forming cavities. As can be appreciated, it is thereforenecessary to provide means for allowing the raw material to flowthroughout the reservoir in order that it may be equally distributedamong the workpiece forming cavities. Because of the nature of theuncured rubber, it is therefore necessary to provide means wherebybottom 50 is permitted to only come within a certain minimum distance ofbottom wall 28, which distance may range from about 0.062 of an inch toas much as 0.125 of an inch. To assure that this distance is maintainedduring each heat of the mold, mechanical stops 56,58 which may beconstructed in any convenient manner, are provided on side wall 30adjacent bottom wall 28 for coaction with bottom 50 of ram C. Oncebottom 50 engages stops 56,58, the raw material flow has been completed.The mold and ram are retained in this closed position while at least thecavities are heated, generally to a temperature of 250 F, or above, tocure the rubber workpieces in the cavities. This curing is done in aknown and accepted manner. Following curing, the mold is movedvertically downward in the direction b of FIG. 1 so that spaces areagain provided between ram C and upper mold half A, and upper mold halfA and lower mold half B. The cured workpieces are then removed from themold cavities for further processing and finishing and the materialremaining in the sprues, runners and reservoir is removed and scrapped.As this material is also cured when the workpieces are cured, there isno present way to reprocess it for any further use.

With particular reference to FIGS. 2 and 3, the subject inventionovercomes the need for using mechanical stops 56,58 and successfullyprovides a reduction in the scrap material generated during each heat ofthe mold. Mold components shown in FIGS. 2 and 3 which are identical tomold components in FIG. 1 have like numerals and new components have newnumerals. In FIG. 2, there is seen upper mold half A which includes topportion 10 having disposed therein reservoir 22 including bottom wall 28and continuous side wall 30. Disposed in bottom wall 28 are 16 sprueholes generally designated 60 which include a smaller diameter portion62 and a generally conical lead-in end portion 64 as is known in theart. These sprue holes are symmetrically spaced in the bottom wall toequalize the forces required and to assure consistent material flow.Disposed between each of these sprue holes, at the lead-in portions, area plurality of channel areas 66 formed directly into bottom wall 28which are open therealong upwardly toward the top of the mold. Althoughthese channel areas may be positioned as required for permitting desiredmaterial flow therealong within the entire reservoir, in the preferredembodiment, each sprue hole is interconnected with its immediatelyadjacent sprue hole by one of these channels. Also in the preferredembodiment, it is seen that these channels extend parallel andperpendicular to each other so as to form generally rectangular patternsin bottom wall 28; however, it will be appreciated that more than onechannel could be used to extend be tween adjacent sprue holes and thatthe channels could also be disposed relative to each other at anglesdifferent than the ones shown in the drawings. It is merely necessary toinclude that number which are so positioned in order to permit thedesired consistent material flow within the reservoir. It has been foundthat a single channel extending between adjacent sprue holes and havinga cross sectional radius of 3/16 of an inch to a depth of O. of an inchis adequate for providing the desired material flow.

As shown best in FIG. 3, and utilizing the same process stepshereinabove described with referenc to FIG. 1, it will be seen thatmechanical stops 56,58 are no longer utilized so that bottom 50 ispermitted to physically contact bottom wall 28. Channels 66 providemeans whereby the raw material (not shown) is permitted to flow withinthe reservoir and between the plurality of sprue holes, even when theram is brought into a closely spaced relationship with bottom wall 28.Thus, the amount of raw material required to be placed in the reservoirto insure desired material flow into the workpiece forming cavities isreduced and substantially the only material remaining following a heatis the material in channels 66 and sprue holes 60. As a practicalmatter, however, sufficient raw material is included with thepredetermined amount initially loaded into the reservoir such thatbottom 50 does not actually contact bottom wall 28 and there is thusformed a thin connecting layer of material formed between the channelsduring the molding process. This extra material assures that all theworkpiece forming cavities will be completely filled during the heat.

The scrap ram flash generated in using the concepts of the subjectinvention is shown in FIG. 4 wherein the material remaining in channels66 following a heat is designated 66, the material remmaining in sprueholes 60 is designated 60' and the thin layer extending between channelscrap 66' is designated 28. Again, this scrap ram flash is notreprocessable as it too is cured during curing of the workpiecesthemselves as hereinabove described. It should be noted that, inpractice, the thickness of portions 28' are often only 0.005 of an inchand the thickness of portions 66' are substantially identical with thedepth of the channels.

In using the previous type of transfer mold arrangement, as describedhereinabove with reference to FIG. 1, approximately percent of theuncured rubber originally placed in the reservoir is discarded asunreprocessable scrap. Although 10 percent may not, at first blush, seemparticularly high, uncured rubber of the type which is commonly used intransfer molding operations costs approximately $3.00 per pound so thatany reduction of this waste will yield substantial savings over a periodof time for high volume jobs. In molds using the-concepts of the subjectinvention, it has been found that there may be realized a to 30 percentreduction in the scrap ram flash generated per heat, or a reduction offrom 2 to 3 percent of the total raw material required. That is, foreach 1,000 lbs. of raw material required when using previous ramtransfer molds, the amount of material required for molds incorporatingthe subject invention provides a material reduction of from 20 to 30lbs. for molding the same number of parts. At $3.00 per pound, thisrepresents a savings of $66 per every 1,000 lbs. of raw materialprocessed. When considering this in light of the fact that many of theparts molded using ram transfer molds are extremely high volume jobs, itwill be appreciated that substantial long term savings will be realized.

The invention has been described with reference to the preferredembodiment. Obviously, modifications and alterations will occur toothers upon the reading and understanding of the specification. It is myintention to include all such modifications and alterations insofar asthey come within the scope of the appended claims or the equivalentsthereof.

Having thus described my invention, I now claim:

3. In a ram transfer mold including a material reservoir having a bottomwall and adjacent side walls, a plurality of sprue holes disposed insaid bottom wall to extend between and interconnect said bottom wall anda plurality of workpiece forming cavities within the mold and a rammember receivable in a close-fitting relationship with said side wallsand spaced from said bottom wall a predetermined minimum distance forpermitting a raw material flow throughout said reservoir and be tweensaid sprue holes whereby said ram forces raw material confined in saidreservoir to flow laterally to and through said plurality of holes andinto the associated workpiece forming cavities to form a ,lurality ofplurality the improvement comprising:

means comprising open channel areas formed in the surface of said bottomwall and interconnecting said sprue holes for permitting flow of saidraw material within said reservoir and between said plurality of sprueholes when said ram is spaced from said bottom wall ess than saidminimum distance.

2. The improvement as defined in claim 1 wherein each said sprue hole isinterconnected with at least each immediately adjacent sprue hole by atleast one of said channel areas.

3. The improvement as defined in claim 2 wherein said sprue holes aresymmetrically spaced in said bottom wall and said channel areas form aplurality of rectangular shaped configurations therein.

4. The improvement as defined in claim 1 wherein said ram contacts saidbottom wall when said ram is moved to said distance less than saidminimum distance.

1. In a ram transfer mold including a material reservoir having a bottomwall and adjacent side walls, a plurality of sprue holes disposed insaid bottom wall to extend between and interconnect said bottom wall anda plurality of workpiece forming cavities within the mold and a rammember receivable in a close-fitting relationship with said side wallsand spaced from said bottom wall a predetermined minimum distance forpermitting a raw material flow throughout said reservoir and betweensaid sprue holes whereby said ram forces raw material confined in saidreservoir to flow laterally to and through said plurality of holes andinto the associated workpiece forming cavities to form a ,lurality ofplurality the improvement comprising: means comprising open channelareas formed in the surface of said bottom wall and interconnecting saidsprue holes for permitting flow of said raw material within saidreservoir and between said plurality of sprue holes when said ram isspaced from said bottom wall ess than said minimum distance.
 2. Theimprovement as defined in claim 1 wherein each said sprue hole isinterconnected with at least each immediately adjacent sprue hole by atleast one of said channel areas.
 3. The improvement as defined in claim2 wherein said sprue holes are symmetrically spaced in said bottom walland said channel areas form a plurality of rectangular shapedconfigurations therein.
 4. The improvement as defined in claim 1 whereinsaid ram contacts said bottom wall when said ram is moved to saiddIstance less than said minimum distance.